Referring to FIG. 42, there is illustrated a conventional discharge lamp lighting device. The discharge lamp lighting device includes an AC power source AC employing a commercial power source; a noise-reducing filter chalk L3 connected in series to one end of the AC power source AC; a rectifier DB formed by a bridge connection of four diodes for the full-wave rectification of an output of the AC power source AC; a DC power source circuit 1 for converting the full-wave rectified output of the rectifier DB into a desired DC voltage; an inverter circuit 2 for converting the DC voltage outputted from the DC power source circuit 1 into a high frequency voltage; a load circuit 3 including at least one discharge lamp La and serving to light the discharge lamp La by using the high frequency voltage supplied from the inverter circuit 2; a chopper control integrated circuit (IC) (e.g., PFC control circuit) 400; an inverter control IC 4; and a control power source E1.
The DC power source circuit 1 includes a series circuit of an inductor L2 and a diode D1 coupled in series to a high-voltage output side of the rectifier DB; a capacitor C4 connected in parallel between the output terminals of the rectifier DB; a switching element Q3 coupled in parallel to the capacitor C4 via the inductor L2; and a smoothing capacitor C3 connected in parallel to the switching element Q3 via the diode D1. The DC power source circuit 1 configured as described serves as a boosting chopper circuit for obtaining the desired DC voltage by chopping the full-wave rectified voltage by way of on-off operating the switching element Q3.
The inverter circuit 2 is of a half-bridge type in which a series circuit of switching elements Q1 and Q2 formed of MOSFETs is connected between both ends of the smoothing capacitor C3. The inverter circuit 2 converts the DC voltage outputted from the DC power source circuit 1 into the high frequency voltage by turning the switching elements Q1 and Q2 on and off alternately.
The load circuit 3 includes a series circuit of a resonance inductor L1, a resonance capacitor C1 and a DC cutting capacitor C2 respectively coupled between a drain and a source of the switching element Q2 at a low voltage side; and the discharge lamp La coupled in parallel to the resonance capacitor C1. The load circuit 3 operates to light the discharge lamp La by using the high frequency voltage supplied from the inverter circuit 2.
The chopper control IC 400 is a PFC (power factor correction) control circuit serving to control an on-off operation of the switching element Q3. The chopper control IC 400 is capable of controlling an output voltage of the boosting chopper circuit regardless of variations in the input voltage or amount of a load and, at the same time, capable of converting a waveform of an input current of the rectifier DB to a sine wave analogous to a waveform of the input voltage. Employed as the chopper control IC 400 is, for example, a general-purpose power-factor improving IC such as MC33262 fabricated by Motorola, Inc.
The inverter control IC 4 includes an inverter (INV) control circuit 44 and a driving circuit 443 to serve as a so-called HVIC (High Voltage IC). The INV control circuit 44 outputs a control signal for controlling an on-off timing of the switching elements Q1 and Q2 of the inverter circuit 2 while the driving circuit 443 outputs a driving signal in response to the control signal provided from the INV control circuit 44 to directly drive the switching elements Q1 and Q2. By turning the switching elements Q1 and Q2 on and off alternately, a state in which power is supplied to the discharge lamp La from the smoothing capacitor C3 and a status in which power is supplied thereto from the DC cutting capacitor C2 are repeated alternately, so that the high frequency voltage is applied to the discharge lamp La, thereby allowing an alternating current of a high frequency to flow into the discharge lamp La.
Further, the inverter control IC 4 has an abnormality detection function for stopping an oscillation of the inverter circuit 2 in response to a detect signal S11 indicating expiration of the lifetime of the discharge lamp La and a dimming function for varying the output of the discharge lamp La in response to an external signal S10. The inverter control IC 4 is formed as a single chip incorporating therein these circuits.
Each of the chopper control IC 400 and the inverter control IC 4 employs a DC low voltage Vcc supplied from the DC voltage source E1 as a power source for operation thereof.
Referring to FIG. 43, there is illustrated a circuit configuration of another conventional discharge lamp lighting device, which is disclosed in Japanese Patent No. 3106592. The circuit configuration therein is substantially identical to that of the conventional device depicted in FIG. 42. Thus, explanations of like parts to those in FIG. 42 will be omitted, and like reference numerals will be used therefor.
In this prior art device, there are employed coils L2a and L2b magnetically coupled to an inductor L2 of a DC power source circuit 1, and source voltages Vcc1 and Vcc2 of a chopper control IC 400 and an INV control IC 4, respectively, are provided from voltages charged into capacitors C10 and C11 from the coils L2a and L2b. 
Further, when the lifetime of a discharge lamp La is exhausted, the INV control IC 4 is reset (initialized) in response to a detect signal S11 serving as a reset signal to thereby stop an oscillation of an inverter circuit 2 while concurrently inputting the reset signal to a chopper control IC 400 as well via a reset circuit 46 to thereby stop a chopper operation of a DC power source circuit 1. As a result, the power consumption of the lighting device can be reduced during a time period when the oscillation is stopped while concurrently contributing to its safety improvement.
In the above-described conventional device, however, it is required to provide the separate ICs 400 and 4 for the control of the DC power source circuit 1 and the inverter circuit 2, respectively, thereby limiting the pattern wiring of a printed circuit board on which these circuit parts are formed. Furthermore, in case of stopping the DC power source circuit 1 when stopping the inverter circuit 2 at a time, e.g., when the lifetime of the discharge lamp La is nearly over, as in the conventional device shown in FIG. 43, a control part for controlling such an operation for stopping the DC power source circuit 1 is additionally required, thereby impeding the miniaturization of the discharge lamp lighting device. Consequently, it is likely that these control circuits are readily affected by external noises, resulting in a malfunctioning or an operational error thereof.
Disclosed in Japanese Patent No. 2001-401532 is a discharge lamp lighting device designed to provide a solution to the above problem. A detailed description of the circuit configuration and the operation thereof will be omitted since they are almost identical to those described with respect to the device shown in FIGS. 42 and 43. However, this third prior art device is distinguishable in that the INV control IC 4 and the chopper control IC 400 are formed as a single IC, thereby performing basic controls required in the discharge lamp lighting device through the use of just one single IC.
The basic controls required in the discharge lamp lighting device are specified as follows:                1) a PFC control for converting a waveform of an input current into a sine wave analogous to a waveform of an input voltage;        2) a timer control for determining an operation status conversion timing of a discharge lamp, e.g., from a preheating status to an ignition voltage application status and, finally, to a lighting status;        3) an inverter output control for determining an output of an inverter circuit in each of the operation statuses;        4) an output correction control for performing a dimming control for varying the output power of the discharge lamp or turning it off depending on a signal inputted from the exterior or by way of detecting a lighting status of the discharge lamp and then performing a feedback thereof; and        5) an abnormality detection control for changing an operational status of each of the above controls by way of detecting a failure of a power supply (or an instant surge of a voltage), an absence of the discharge lamp, and the remaining lifetime of the discharge lamp.        
By implementing all these basic controls through the use of only one control IC, it becomes easier to mount each circuit element of the discharge lamp lighting device and form a pattern wiring on a printed circuit board. In addition, each control circuit of the lighting device can be protected against the external noises, so that a delay of an abnormality control signal that is provided as a control measure for an operational error can be prevented. Furthermore, an excessive stress imposed on each circuit element can be greatly reduced, thereby contributing to the miniaturization of the discharge lamp lighting device without causing any deterioration in functions required therein.
Recently, however, a further advanced control mechanism is required in a discharge lamp lighting device, and in a lighting apparatus and a lighting system employing the same. Japanese Patent Laid-open Publication No. 2001-15276 discloses one exemplary lighting apparatus employing such an improved control mechanism. FIG. 44 shows a circuit configuration thereof. A discharge lamp lighting device U1 illustrated in this apparatus employs a boosting chopper circuit and an inverter circuit, as in the above-described conventional examples, to thereby supply a high frequency power outputted from the inverter circuit to a discharge lamp La. Further, the power supplied to the discharge lamp La can be adjusted by varying an on/off cycle of switching elements Q1 and Q2. A unit U2 having a lighting period detecting unit 13 and an illumination correcting system 15 sends a dimming signal to the discharge lamp lighting device U1. The lighting period detecting unit 13 detects the voltage of an AC power source AC by a resistance type potential division and measures a time period during which the voltage of a smoothing capacitor C8 coupled to output terminals of a rectifier DB2 is maintained above a predetermined level by using a lighting timer 14. The illumination correcting system 15 and the lighting timer 14 may be implemented by employing a microcomputer. Incorporated in the microcomputer is a non-volatile memory 17, e.g., an EEPROM for reading and storing the time period measured by the lighting timer 14 and, further, storing therein a correction table employed by the illumination correcting system 15. The correction table defines an illumination rate for correction corresponding to duration of using the discharge lamp La. An illumination rate setting unit 18 included in the illumination correcting system 15 determines an illumination rate of the discharge lamp La by reading it from the non-volatile memory 17 by using the duration of use detected by the lighting timer 14.
FIG. 45 provides a flow chart for describing the above-described operations. Though the luminous flux of the discharge lamp La decreases due to the aging thereof as the duration of use increases as shown in FIG. 46A, the output power of the discharge lamp La can be maintained substantially constant as shown in FIG. 46C by way of performing a dimmed lighting for a certain period of time immediately after a replacement of the discharge lamp La and then gradually increasing the output power to a full lighting level while measuring the duration of use, as can be seen in FIG. 46B. Such an operation may prevent the output power of the discharge lamp La from being decreased due to the aging thereof and, further, an energy saving can be achieved, for the discharge lamp La is lighted dimly for the certain period after being replaced.
Hereinafter, there will be described a reset process of resetting data stored in the EEPROM for storing the time period measured by the lighting timer 14. The present example executes such resetting processes as follows:
(1) the data is reset when a result of detecting a voltage across both ends of the discharge lamp La reveals that the lifetime thereof has elapsed;
(2) the data is reset when it is found that the current status is a no-load status by detecting whether or not the discharge lamp La is connected to the lighting device;
(3) the data is reset when no AC power source AC is supplied to the lighting device and thus the current status is determined as a no-load status; and
(4) the data is reset by a reset switch mechanically operated by a user of the lighting apparatus.
In the ensuing discussion, problems occurring when performing the above resetting processes will be described.
In the resetting process (1), resetting is performed when, by detecting the voltage across both ends of the discharge lamp La, it is found that the lifetime of the discharge lamp has elapsed. Since, however, the lighting time detecting circuit for detecting the lighting period of the discharge lamp La and the circuit for detecting whether or not the lifetime of the discharge lamp La has elapsed are implemented as separate circuit elements, the number of parts required is increased, hampering the size reduction of the discharge lamp lighting device.
Further, in case the control IC described above has a function for stopping an inverter operation by detecting the lifetime of the discharge lamp, the resetting of the memory data of the EEPROM should be completed before stopping the operation of the inverter at a point of time when the lifetime of the discharge lamp has almost exhausted. However, since respective criteria based on which the discharge lamp lighting device and the illumination rate correction device detect the lifetime of the discharge lamp are different from each other, the data of the EEPROM may be reset well in advance of the elapse of the lifetime. After the resetting of the data, the discharge lamp lighting device is lighted as in the initial stage of the lifetime (see FIG. 46B), which makes it difficult to control the output power of the discharge lamp lighting device to be constant.
Furthermore, in case the control IC described above has a function for stopping the inverter in a no-load status in which the discharge lamp is not connected to the lighting device, there is a likelihood that the time period measured by the lighting timer is stored as a wrong value since it is impossible to distinguish a state where the discharge lamp is lighted by the operation of the inverter circuit from the no-load status where the operation of the inverter is stopped. Accordingly, it is required to additionally install a circuit for detecting the no-load status in the lighting timer for detecting the lighting period in order to determine, based on a detect signal provided from the no-load status detecting circuit, whether to stop the timer operation or stop writing the lighting period into the EEPROM in the state where the operation of the inverter circuit is stopped. As a result, the number of parts required increases to thereby make a wiring complicated on the printed circuit board.
In the resetting process (2), resetting is carried out when the discharge lamp is found to be in a no-load status by checking a connection of the discharge lamp to the lighting device. However, as in the resetting process (1), since the lighting timer for detecting the lighting period and the circuit for detecting the no-load status are two separate circuits, the number of parts required increases, thereby impeding the size reduction of the discharge lamp lighting device.
Further, in case the control IC described above has a function to stop the operation of the inverter by detecting the lifetime of the discharge lamp, it is possible that the time period measured by the lighting timer is stored as a wrong value, as in the resetting process (1), since it is impossible to distinguish a state where the discharge lamp is lighted by the operation of the inverter circuit from a state where the operation of the inverter is stopped at a time when the lifetime of the discharge lamp has nearly elapsed.
Moreover, if the lamp is replaced with a new one while an AC power source is turned off, the data stored in the EEPROM cannot be reset and, thus, a predetermined output power of the discharge lamp may not be obtained. Further, since there is required a battery means for supplying a stable source voltage to the no-load detecting circuit and the illumination correcting system within the discharge lamp lighting device in order to reset the data of the EEPROM in a no-load state regardless of the supply from the AC power source, the size of the discharge apparatus and costs involved become increased.
In the resetting process (3), the data is reset when it is found that the current state is a no-load state where the AC power source AC is not provided to the lighting device. However, it also requires a battery means for supplying a stable source voltage to the no-load detecting circuit and the illumination correcting circuit within the discharge lamp lighting device, as in the case of the resetting process (2).
Meanwhile, the resetting process (4) is directed to performing a reset by using a mechanically operated reset switch. Japanese Patent Laid-Open Publication No. 2001-338783 discloses a lighting apparatus of this type, which is illustrated in FIG. 47. As shown therein, a reset switch S2 is installed on a surface of a main body 50 of the lighting apparatus and is connected to a discharge lighting device 54 via a wiring 53. Though using the reset switch S2 in the discharge lamp lighting device incorporating therein the control IC described above is advantageous in that the data of the EEPROM can be securely reset regardless of functions set in the control IC, there still remain problems related to, e.g., an installation of the switch S2, the wiring 53 between the switch S2 and the discharge lighting device 54, and a connection of the wiring 53 to the discharge lighting device 54.